The present invention relates generally to fuse holders and, more particularly to cartridge fuse holders capable of rejecting improper fuses.
Cartridge fuses are available in a variety of current ratings and interrupting capacities (IC). At least in one case, cartridge fuses of the same current rating but of different interrupting capacity are of substantially the same physical size. Specifically, the current limiting, high IC class R cartridge fuse is essentially identical in physical dimensions to the non-current limiting, low IC class H cartridge fuse. Consequently, the class H and class R fuses are interchangeable insofar as the fuse holder is concerned. Obviously, they are not interchangeable from the standpoint of circuit protection. If a class H fuse is inadvertently inserted in a fuse holder installed in a circuit calling for class R fuse protection, a potentially hazardous situation is created. To discourage this from occurring, industry has resorted to keying one end terminal of the class R fuse and a specially designed rejection fuse holder which accepts the keyed end terminal of a class R fuse but does not accept the unkeyed end terminal of a class H fuse. In the case of class R fuses having ferrule type end terminals, keying is achieved by machining an appropriately dimensioned annular groove in one of the terminal ferrules. The rejection fuse holder is then provided with an interference member which is accommodated in the annular groove of a class R fuse terminal ferrule as it is inserted between the clamping arms. The interference member engages the ungrooved, smooth periphery of a class H fuse terminal ferrule to obstruct its insertion between the clamping arms. Rejection fuse holders of this type are exemplified in U.S. Pat. Nos. 2,943,295; 3,914,005; 3,960,435; 3,984,801 and 4,017,816.
Since both class R and class H fuses are widely used, manufacturers are forced into the uneconomical proposition of having to manufacture and stock both the rejecting and the non-rejecting types of fuse holders. Since the fuse holders are assembled in electrical equipment prior to shipment, the equipment itself must also be stocked or, alternatively, the type of fuses the equipment is to utilize must be known at the time of assembly.
To mitigate the additional manufacturing expense engendered by the necessity of supplying both types of fuse holders, manufacturers have resorted to providing with the equipment a basic non-rejecting type fuse holder capable of accepting both class H and class R cartridge fuses and offering a kit including a rejection member which is physicaly adapted to the fuse holder by the customer at the time the equipment is installed. Examples of this approach are illustrated in the above cited U.S. Pat. Nos. 3,984,801 and 4,017,816. Of course, requiring the customer to assembly a rejection member to a fuse holder in the field involves some time and effort typically on the part of relatively high-salaried electricians, and thus this approach constitutes an added expense to the customer over and above the cost of the kit. Since the electrical equipment involved typically has a plurality of fuse holders, the additional customer expense is not insignificant. Moreover, since the rejection member is assembled to the fuse holder in the field, the ability to readily defeat the rejection feature through subsequent disassembly of the rejection member becomes difficult to discourage. The inability to readily defeat a fuse rejection feature once it has been implemented is an Underwriters Laboratories requirement.
It is accordingly an object of the present invention to provide a fuse holder assembly which is readily field convertible from a fuse non-rejecting mode to a fuse rejecting mode.
A further object of the present invention is to provide a fuse holder assembly of the above character which, upon being converted from its non-rejecting mode to its rejecting mode, cannot be readily converted back to its non-rejecting mode.
Another object of the present invention is to provide a fuse holder assembly wherein the conversion from non-rejecting to rejecting modes does not require the addition of any structural elements to the assembly.
An additional object of the present inventon is to provide a fuse holder of the above character which is inexpensive to manufacture and is convertible from its non-rejecting to its rejecting modes with minimal time and effort.
Other objects of the invention will in part be obvious and in part appear hereinafter.